Can we please spare the English language these grammatical atrocities once and for all?
Sentence example: They're waiting in their car over there.
This trio tops of the list of most commonly misused words in the English language. "Their" is a possessive pronoun which serves as the plural equivalent of "his" or "her" (and "its" too) while "there" is an adverb used to indicate a certain location where the speaker is not, just like "here" is used to refer to the place where the speaker is. "They’re," on the other hand, is simply a shortened form (contraction) of "they are."
Sentence example: Go rest in your room if you're still tired.
"You're" is a contraction of "you" and "are" while "your" is a possessive pronoun. But people often tend to confuse the two, notably in the course of online communication. When in doubt, try using "you are" in your sentence instead. If the sentence still makes sense, then "you're" is eventually the correct alternative and vice versa.
"Quiet" is an adjective that means "silent" or "discreet" while "quite" is an adverb that indicates the extent or degree of something (could mean absolutely/totally or else fairly/somewhat, depending on the context).
"Its" is a possessive pronoun while "it's" is a contraction of either "it is" or "it has." Try formulating your sentence using "it is" when in doubt. If the sentence sounds incorrect, then "its" is most probably the correct alternative.
To "lose" something is to not be able to have it/find it (it eventually becomes lost). The adjective "loose," however, is used to refer to something that is not tight (as in clothing) or not tightly fixed in place (a knot for instance) while the verb "loose" means to set free or release.